1. Field of the Invention
The present invention relates to a linear scale that is used for displacement measurement.
2. Description of the Related Art
A detector that reads graduation and a graduated scale are used for displacement measurement in the art. The scale is typically provided with a scale table and graduations. The scale table is made of glass or ferrous metal. The graduations are formed on the upper surface of the scale table. Therefore, a change in the form of the scale table has a negative influence upon measurement accuracy. For example, the dimension of the scale may change with time due to stress strain caused by thermal stress applied for a short time or stress release for a long time.
For example, a scale disclosed in Japanese Unexamined Patent Application Publication No. 2007-183254 has been proposed to address the above problems. The scale disclosed in the above patent document is provided with a holder under the scale table (i.e., scale plate). The holder can be mounted on a predetermined surface. The holder fixes the scale table at a Bessel point by means of an elastic adhesive. That is, in the structure of the scale disclosed in the above patent document, the holder absorbs a change in the form of the scale table.
However, the structure disclosed in the above patent document has a disadvantage in that it requires the holder. In addition, it is necessary to determine a fixation place with high positional accuracy. Therefore, it is disadvantageous in terms of manufacturing cost.